This invention relates to a cyclone separator. It relates more particularly to a two-stage hydrocyclone for separating immiscible fluids, e.g. fluids generated in the oil industry, such as produced water and high water-cut production fluids.
In heavy oil production, it is commonplace for fluids produced at the well head to contain in excess of 70% by volume of water, as well as varying amounts of suspended solids. In order to transport and process the oil and safely dispose of or recycle the water, it is necessary to separate these components in an efficient manner.
A variety of different cyclone separators have been developed for this purpose. For instance, Thew et al. U.S. Pat. No. 5,017,288 describes a cyclone separator for removing oil from water having a first cylindrical section followed by a pair of converging funnel shaped sections. The oil is removed through an overflow outlet at a closed end of the cylindrical section, while the water travels down the funnel shaped section.
In Coleman and Thew, U.K. Patent Application 2,107,616 published May 5, 1983, a similar type of hydrocyclone is described in which the overflow outlet includes a retractable plug for changing the size of the outlet.
Kuryluk U.S. Pat. No. 5,564,574 describes a separator for separating materials of different specific gravities, including materials of non-uniform size. That system employs a rotating agitator as a primary means of imparting rotational energy to the materials being processed. It also depends on separate injection of water and separate chambers for mixing and dilution.
A still further improvement to the design of hydrocyclones is provided in Hashmi et al. U.S. Pat. No. 5,828,237 and WO 98/48942, published Nov. 5, 1998.
Such hydrocyclones have proven to be highly effective in separately oily fluids. They are single stage hydrocyclones designed to produce two product streams: an overflow of concentrated oil and an underflow of clean water. However, because the optimum operating conditions for obtaining the two product streams are different, the quality of one of the two products must be compromised in the single-stage hydrocyclone system.
It is the object of the present invention to provide a further improved hydrocyclone system capable of providing two optimum product streams.
In accordance with the present invention, a hydrocyclone system has been developed which is capable of optimizing both product streams. This is achieved by way of a two-stage hydrocyclone system in which the first stage hydrocyclone is set up to produce a concentrated oil stream, while the second stage hydrocyclone is set up to optimize the production of clean water from the dirty water underflow stream of the first stage hydrocyclone.
The cyclone separator used in each stage is similar in type but may vary in size, e.g. the second stage may be smaller and of lower capacity than the first stage. Each stage comprises a generally cylindrical first portion or involute with an open end and a closed end, a generally axial overflow outlet in the closed end and at least two radially balanced feed ejection ports in the cylindrical first portion adjacent the closed end. A converging tapered second portion with open ends is axially flow connected to the open end of the cylindrical first portion and a converging tapered third portion with open ends is axially flow connected to the tapered second portion. A fourth generally cylindrical portion is axially flow connected to the tapered third portion. For operation within the present invention, the second stage cyclone separator has a longer cylindrical fourth portion than does the first stage.
The first and second stage hydrocyclones are mounted within a horizontally elongated pressure vessel comprising at least five chambers separated from each other by divider walls. These chambers include a feed inlet chamber, a concentrated oil overflow chamber, an underflow/feed chamber, a dirty water overflow chamber and a clean water underflow chamber.
The first stage hydrocyclone extends through a divider wall between the feed inlet chamber and the underflow/feed chamber. The axial overflow outlet of the first hydrocyclone flow connects to an opening in the divider wall between the feed inlet chamber and the concentrated oil overflow chamber and the downstream end of the fourth generally cylindrical portion of the hydrocyclone is positioned to flow into the underflow/feed chamber. This first hydrocyclone is arranged to pass through the axial overflow outlet a concentrated oil stream that is substantially free of water. A water stream containing some oil is collected in the underflow/feed chamber. This underflow/feed chamber also serves as the feed chamber for the second hydrocyclone stage.
The axial overflow outlet of the first cylindrical portion of the second stage hydrocyclone flow connects to an opening extending through the divider wall between the underflow/feed chamber and a dirty water overflow chamber. This second stage hydrocyclone is longer than the first stage hydrocyclone and extends through at least two divider walls with the outlet of the fourth generally cylindrical portion of the second stage hydrocyclone feeding into a clean water underflow chamber.
With the system of the present invention, it is possible to operate at a sufficiently high pressure such that the oil and water underflow from the first stage hydrocyclone has sufficient pressure to continue on its journey through the second stage hydrocyclone. While this is a preferred arrangement, it is also possible to use a booster pump to raise the pressure of the feed stream to the second hydrocyclone stage.
According to a preferred embodiment, both the first stage and second stage hydrocyclones pass through an intermediate chamber containing a heated fluid for heating the material passing through the hydrocyclones. This reduces viscosity and enhances separation.